1. Field of the Invention
The present invention relates to a method of making an integrated stator, a radial core type brushless direct-current (BLDC) motor using the integrated stator, and a method of making the radial core type brushless direct-current (BLDC) motor, and more particularly, to a brushless direct-current (BLDC) motor having a radial core type double rotor structure which can greatly enhance productivity of assembling a stator in which coils are sequentially wound on a plurality of division type stator cores in a continuous winding method, and a plurality of interconnected stator core assemblies are automatically located and set using positioning grooves which are formed in a mold itself to then be injection-molded at an insert molding mode.
2. Description of the Related Art
BLDC motors are classified into a core type (or radial type), which has a generally cup-shaped (or cylindrical) structure, and a coreless type (or axial type), according to whether or not a stator core exists.
BLDC motors of a core type structure are classified into an internal magnet type including a cylindrical stator where coils are wound on a number of protrusions formed on the inner circumferential portion thereof in order to form an electronic magnet structure, and a rotor formed of a cylindrical permanent magnet, and an external magnet type including a stator where coils are wound up and down on a number of protrusions formed on the outer circumferential portion thereof, and a rotor formed of a cylindrical permanent magnet on the outer portion of which multiple poles are magnetized.
In a conventional external magnet type BLDC motor, a main path of a magnetic flux is a magnetic circuit which forms a closed circuit starting from a permanent magnet of a rotor and proceeding again toward the permanent magnet and a yoke via a gap and the stator core of a stator.
In a conventional internal magnet type BLDC motor, a plurality of T-shaped core portions on a stator core around which coils are wound, protrude inwards. Also, the inner longitudinal sections of the respective core portions form a circle of a predetermined diameter to thereby make the core portions form a cylinder. Also, a rotor having a cylindrical permanent magnet including a rotational shaft, or a ring-shaped permanent magnet attached to a cylindrical yoke including a central rotational shaft, is mounted in the inner portion of the cylinder surrounded by the core portions. The internal magnet type BLDC motor rotates in the same manner as that of the external magnet type BLDC motor.
The magnetic circuit in the above-described core type BLDC motor has a symmetrical structure in the radial direction around the rotational shaft. Accordingly, the core type BLDC motor has less axial vibrational noise, and is appropriate for low-speed rotation. Also, since a portion occupied by a gap with respect to the direction of the magnetic path is extremely small, a high magnetic flux density can be obtained even if a low performance magnet is used or the quantity of magnet to be used is reduced. As a result, a big torque and a high efficiency can be obtained.
However, such a core, that is, a yoke structure causes big loss of a yoke material when fabricating a stator. In addition, a special-purpose expensive dedicated winding machine should be used for winding coils around the yoke during mass-production, because the yoke structure is complicated. Also, since a mold for fabricating a stator is expensive, initial investment costs become high.
In the core type AC or BLDC motor, especially, in the core motor of the radial type, it is very important factor for determining a competitive power of motors, to make the stator core configured into a complete division type, since coils can be wound on division type cores with a high efficiency using a general purpose winding machine which is cheaper than a special-purpose expensive dedicated winding machine. On the contrary, since a low efficient winding is made using the expansive dedicated winding machine, in the case of an integrated stator core structure, a manufacturing cost for the motors becomes high.
In order to employ the advantages of the axial double rotor type and the radial core type and improve the disadvantages thereof, a radial core type double rotor structure BLDC motor has been proposed in Korean Patent No. 432954 to the same applicant.
In the Korean Patent No. 432954, rotors including respective permanent magnets are disposed in both the inner and outer sides of a stator core to thereby form flow of a magnetic path by the permanent magnets and the rotor yoke. It is thus possible to divide the stator core completely into a plurality of stator core portions. Accordingly, productivity of the stator core and power of the motor can be greatly heightened through an individual coil winding process.
Moreover, in the Korean Patent No. 432954, a plurality of division type core assemblies around which coils have been wound are prepared, and then the plurality of division type core assemblies around which coils have been wound are arranged and fixed on a printed circuit board (PCB). Then, the coils are connected and thereafter the plurality of division type core assemblies around which coils have been wound are molded in an annular form using an insert molding process using a thermosetting resin, to thus prepare an integrated stator.
However, when a plurality of individual cores are integrally assembled to thereby mutually connect coils, in the Korean Patent No. 432954, an assembling structure and method of the stator which can be effectively assembled have not been presented.
As described above, the coil winding of the individual division core is more greatly excellent in its productivity than that of the case of using the integrated (that is, single) core when implementing the stator core into a plurality of division type cores. However, there is a structural problem of lowering a productivity and durability thereof when the plurality of division type cores are assembled.
Taking such points into consideration, Korean Patent No. 545848 discloses a structure of enhancing an assembly productivity of a stator, including an annular core support plate which a plurality of stator core assemblies around a bobbin of which coils are wound are accommodated in and supported to at a regular interval, and a plurality of coils are wired by electric phases, and an automatic positioning/supporting unit for automatically positioning and supporting the plurality of stator core assemblies in and to the core support plate.
In the Korean Patent No. 545848, a plurality of division type core assemblies which are obtained by winding coils around each division type core are assembled in the core support plate, and the respective core assemblies are electrically interconnected in the core support plate. In this case, since the wound coils should be connected to connection pins and the connection pins should be coupled to conductive lines formed in the core support plate in the bobbin of each division type core, an assembly productivity is lowered.
Therefore, preferably, it is required to integrate a plurality of stator cores in which coils are wound with an insert molding process using a thermosetting resin without using the annular core support plate as described above.
In the meantime, a general large-sized motor has a structure in which a plurality of stator poles and a plurality of rotor poles are combined with each other. In the case of a division core type, a continuous winding which is made on a number of groups of cores composed of a plurality of division type cores is more preferable than an individual winding/assembly which is made on a plurality of division type cores in view of an assembly productivity.
However, the known general purpose winding machine has a structure of winding coils as a single bobbin is mounted in a single spindle to then make the spindle rotate. Accordingly, continuous windings cannot be made on a number of groups of cores composed of a plurality of division type cores, or a plurality of division type cores.
In the meantime, a stator core is generally made by molding a plurality of silicon steel plates of 0.35-0.5 mm thick in a predetermined shape, and laminating the molded results. In the case of an integrated core type, a magnetic flux density is not uniform at the air gap due to the influences of slots for winding coils to thereby generate a cogging torque phenomenon and a torque ripple phenomenon for which the torque is not regular. In order to reduce the cogging torque and the torque ripple, a number of slots should be formed in the stator cores, or auxiliary salient poles or auxiliary slots should be formed in the stator core. Otherwise, the stator core employs a skew structure.
However, the integrated stator core employing the skew structure has the problem that its coil winding is more difficult than that of the stator core which does not adopt the skew structure. When a skew is given to a core in the division type stator core structure so that the division type core itself is divided to form a structure of a motor, that is, a stator, it is impossible to perform coupling between the cores.
In the meantime, in the case of the motor disclosed in the Korean Patent No. 545848, a plurality of cooling holes for cooling the coils of the stator inserted between the rotor supporters are formed in the rotor supporters. The rotor supporters and bushings are connected therebetween with a plurality of radially extending ribs.
However, a plurality of radially extending ribs connecting between the rotor supporters and the bushings do not have enough support strength and thus there is a need to reinforce the plurality of radial ribs. The plurality of simple cooling holes for cooling the coils of the stator formed in the rotor supporters do not induce an effective flow of the air.